It is known to digitize handwriting by determining the movement of a pen that is used for providing the handwriting. The movement may e.g. be determined by one or more accelerometers mounted to the pen. Another alternative is to use a base with a position code and to provide the pen with a sensor which records the position code locally at the tip of the pen during the pen's movement over the base. A processing unit, arranged in the pen or externally thereof, can then decode the position code to a series of position indications, e.g. coordinates, which reflects the pen's movement over the base.
WO 01/26033, U.S. Pat. No. 5,477,012, WO 00/73983 and WO 92/17859 disclose different examples of position codes that could be used for recording handwriting.
Moreover, WO 01/75779 discloses a form provided with a position code enabling digital recording of information written on the form. In addition to the position code, the base is here provided with a form layout, such as frames around entry fields and text indicating what information should be filled-in in the entry fields.
According to WO 01/75779, the form layout can be printed on the base simultaneously with the position code or in different runs. In order not to disturb the reading of the position code, different printing inks should be used for the form layout and the position code. The printing ink for the form layout should moreover be invisible for the sensor in the pen. If both the printing code and the form layout are printed with the same printing ink, the form layout may partly obscure the printing code, making it impossible to decode the position code in areas close to the form layout or in areas obscured by the form layout.
However, the use of different printing inks is unpractical. It would be more practical if the pen could be used on forms printed on blank papers by means of a monochrome printer, e.g. a monochrome laser printer.